1. Field of the Invention
The present invention relates to belt drive systems.
2. Description of the Prior Art
Belt drive systems have been proposed comprising a flat belt which has a one-layer helically wound cord as a tension element. During operation of such a system, the belt tends to move in an axial direction and thus to free itself from the pulleys, shafts or the like over which it passes. This axial movement can be prevented by the use of convex driving pulleys, driving shafts and the like, of which the manufacture, however, is fairly costly. They also have the disadvantage that the convexity of the pulley gives rise to different peripheral speeds, which in turn involve forced slipping movements of the driving belt and internal tensions in the belt body. Restriction of the axial movement can be effected by the use of edge discs on the shafts, but this, on the other hand, is disadvantageous because there is continuous friction between the side of the driving belt and the side of the disc, and this can produce premature damage to the tension element, particularly in the case of flat belts of which the sides are not specially protected.
Belt drive systems have also been proposed in which the belt consists of a flat belt part with a helically wound tension element and tooth-shaped transverse ribs arranged on the contact side, which engage in correspondingly formed slots in the shafts, pulleys and the like to produce a positive connection. Such belts also produce an axial movement which is likewise usually restricted by the use of a costly edge disc arrangement. Belts having a flat belt part with a helically wound tension element, and wedge-shaped ribs arranged on the contact side, have also been proposed. In such a belt, each side of each rib contacts the sides of corresponding wedge-shaped grooves of the pulleys, shafts and the like, and this belt has the disadvantage that the rib angle must be adjusted to the coefficient of friction that is present in each case, in order to prevent self-locking and consequent premature destruction. On the other hand, because of their multiple groove and therefore multiple rib design, such drive systems require a particularly precise adjustment in respect of their groove and belt spacing, and their manufacture is correspondingly costly. Further, this belt is particularly disadvantageous as regards the action of foreign bodies, because foreign bodies up to a certain particle size that have fallen into the drive system, will fall out of the system only under favourable conditions, and in cases of jamming between the wedge-shaped ribs, premature destruction of the belt can occur.